Method for detecting an electrical defect of contact/via plugs

ABSTRACT

A method for detecting an electrical defect of contact/via plugs is provided. In the method, the contact/via plugs are monitored by an electron-beam (E-Beam) inspection tool to capture an image with a VC (voltage contrast) difference, and then an image extraction is performed on the image with the VC difference, wherein the image extraction is based on Target gray level/back ground gray level. The extracted image is contrasted with a layout design base to obtain a blind contact or Quasi-blind issue of contact/via plugs. A grayscale value of the VC difference having the blind contact or Quasi-blind issue is compared with a determined range of grayscale value to determine whether the VC difference is abnormal.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to an analytical technique of a chip, and moreparticularly, to a method for detecting an electrical defect ofcontact/via plugs.

2. Description of Related Art

Die to die inspection is widely used inspection methodology, this methodis to capture the defective optical, SEM or patch image in inspectingdie and then compare with the other die reference image at the exactlysame location in real time. However, as the technology node shrinks to40 nm and beyond, it is hard to use large inspection field to inspectthe tiny defects in electron beam (E-beam) inspection.

The E-Beam inspection (EBI) tool is currently used to obtain the imageof the surface structure of a chip. Voltage contrast (VC) inspection inEBI is widely utilized to capture electrical defects of contact/viaplugs. The monitoring of VC variations in the via plugs are morecomplicated than that of contact plugs because the via plugs layoutstructure connecting with different pitches, length metal lines andmetallic layers.

Therefore, it needs to develop method for the technology node shrinkage.

SUMMARY OF THE INVENTION

The invention provides a method for detecting an electrical defect ofcontact/via plugs.

The invention further provides a method for detecting an electricaldefect of contact/via plugs so as to avoid misalignment issue.

An exemplary embodiment of the present invention includes a method fordetecting an electrical defect of contact/via plugs. In the method, thecontact/via plugs are monitored by an electron-beam (E-Beam) inspectiontool to capture an image with a VC (voltage contrast) difference, andthen an image extraction is performed on the image with the VCdifference, wherein the image extraction is based on target graylevel/back ground gray level. The extracted image is contrasted with alayout design base to obtain a blind contact or Quasi-blind issue of thecontact/via plugs. A grayscale value of the VC difference having theblind contact or Quasi-blind issue is compared with a determined rangeof grayscale value to determine whether the VC difference is abnormal.

In one embodiment of the invention, a pixel size of the E-Beaminspection tool is less than 0.1 μm.

Another exemplary embodiment of the present invention includes a methodfor detecting an electrical defect of contact/via plugs. In the method,a hot spot inspection, a leap and scan inspection, or a continuous scaninspection is used to monitor the contact/via plugs for capturing a VCdifference, and then an image extraction is performed on the image withthe VC difference, wherein the image extraction is based on targetground/back ground gray level. The extracted image is contrasted with alayout database to obtain a blind contact or Quasi-blind issue of thecontact/via plugs. A grayscale value of the VC difference having theblind contact or Quasi-blind issue is compared with a predeterminedrange of grayscale value to determine whether the VC difference isabnormal.

In another embodiment of the invention, the hot spot inspection, theleap and scan inspection, and the continuous scan inspection eachcomprise locating same coordinates in a design chip with different dies.

In another embodiment of the invention, the contact/via plugs are bothat periphery and array circuits of the different dies, and the peripherycircuit is around the array circuit.

In another embodiment of the invention, a pixel size of the hot spotinspection is less than 0.1 μm.

In another embodiment of the invention, a pixel size of the leap andscan inspection is less than 0.1 μm.

In another embodiment of the invention, a pixel size of the continuousscan inspection is less than 0.1 μm.

In one embodiment of the invention, the image extraction furthercomprises revising tone of the captured image.

In each embodiment of the invention, the extracted image may be asemi-circular image, a reduced image, or nothing.

In each embodiment of the invention, the predetermined range ofgrayscale value is between 55 and 130.

In each embodiment of the invention, the layout design base includes alayout containing conductive lines under the contact/via plugs. Thepredetermined range of grayscale value is dependent on different size ofthe conductive lines connected to the contact/via plugs, wherein thesize of the conductive lines contains length, width, area or pitchthereof.

In each embodiment of the invention, the image extraction is utilized toobtain contours of the conductive lines under the contact/via plugs.

Based on the above, according to the invention, the electrical defect ofcontact/via plugs may be correctly determine, even the Quasi-blindissue. Moreover, the hot spot inspection of the invention is excellentin alignment performance and sensitivity.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary, and are not intendedto limit the scope of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the invention, and are incorporated in and constitute apart of this specification. The drawings illustrate embodiments of theinvention and, together with the description, serve to explain theprinciples of the invention.

FIG. 1 is a flowchart of detecting an electrical defect of contact/viaplugs according to the first embodiment of the invention.

FIG. 2A illustrates the contours of normal contact/via plugs.

FIG. 2B illustrates the contours of abnormal contact/via plugs.

FIG. 3A is a layout containing metal lines under via plugs.

FIG. 3B illustrates the VC of the via plugs in FIG. 3A.

FIG. 4A shows a layout contains metal lines under via plugs according toan example of the first embodiment.

FIG. 4B shows the VC differences of a chip after forming the via plugsof FIG. 4A.

FIG. 4C is a FIB (Focused Ion Beam) image illustrating the via plugs andthe contact plugs along line C-C in FIG. 4A.

FIG. 5 is a flowchart of detecting an electrical defect of contact/viaplugs according to the second embodiment of the invention.

FIG. 6A shows an image obtained by leap & scan with positive mode.

FIG. 6B shows an image obtained by the hot shot inspection of the secondembodiment.

DESCRIPTION OF THE EMBODIMENTS

FIG. 1 is a flowchart of detecting an electrical defect of contact/viaplugs according to the first embodiment of the invention.

In step 100, the contact/via plugs are monitored by an electron-beam(E-Beam) inspection tool to capture an image with a VC difference in thecontact/via plugs. In the embodiment, a pixel size of the E-Beaminspection tool may be less than 0.1 μm. For example, the small pixelsize may be accomplished by using narrower aperture to converge theelectron beam. The generation of the VC differences is affected by theelectrical field condition caused by the surface charging voltage. Forexample, when the E-beam is emitted on the surface of each contact/viaplug, the numbers of secondary electrons are different between thenormal contact/via plugs and blind contact/via plugs. Under positivecharged mode condition, the brightness of a SEM image at defectivecontact/via plugs become darker than that of a normal contact/via plug.On the contrary, if two neighboring contact/via plugs suffer the shortand leakage issue, it will become brighter than that of normalcontact/via plug.

After the step 110, in step 110, an image extraction is performed on theimage with the VC difference. The image extraction is based on targetgray level/back ground gray level. Moreover, if necessary, the imageextraction further includes revising tone of the captured image in thestep 100. Since the image extraction can extract a contour of extractedimage, the contact/via type can be judged by the contours thereof. Ifthe extracted image is a semi-circular image, a reduced image ornothing, it could be regarded as abnormal contact/via plug. For example,through the image extraction, the blind contact/via plugs shows nothing,and the dark (i.e. defective contact/via plugs) is small. FIG. 2Aillustrates the contours of normal contact/via plugs, and FIG. 2Billustrates the contours of abnormal contact/via plugs. It is noted thatthe contact/via plug 200 in FIG. 2A does not appear in FIG. 2B, there isa blind contact/via plug in FIG. 2B.

In the embodiment, an instrument may be utilized to perform the imageextraction, such as a critical dimension scanning electron microscope(CD-SEM), an electron-beam (E-Beam) inspection tool, a bright-fieldinspection tool with wavelength 150-800 nm, or a dark-field inspectiontool with laser light source. The method of the image extraction, forexample, includes Edge contour extraction, Self-Affine mapping system,Self-Affine snake model, Active contour model, expectation-maximisationalgorithm, Principal component analysis, Level set algorithm, or MonteCarlo techniques.

Thereafter, in step 120, the extracted image is contrasted with a layoutdesign base to obtain a blind contact or Quasi-blind issue of thecontact/via plugs. For example, the layout design base comprises alayout containing conductive lines under the contact/via plugs. Inaddition, the image extraction is performed on the conductive linesunder the contact/via plugs to obtain their contours. According toresearch from the invention, it is found that the VC of each contact/viaplug is dependent on its located environment. For example, in FIG. 3A,it demonstrates the layout 300 containing metal lines 302 a-d under viaplugs 304 a-d, and the via plugs 304 a-d are located at metal lines 302a-d with different length. FIG. 3B illustrates that the via plugs 304a-b located at short metal lines 302 a-b show much lower VC than that oflocated at large-area metal line 302 c or long-stripe metal line 302 d.Therefore, the VC of the via plugs 304 a-b is lower than that of the viaplugs 304 c-d. In other words, with aid of contact/via layout designbase and the image extraction, the blind contact or Quasi-blind issuebecomes easier to distinguish according the correlation of via pluglocations. Except for length or area of the metal lines 302 a-d, widthor pitch of the metal lines may be also utilized to distinguish theblind contact or Quasi-blind issue. Moreover, if the plugs are contactplugs, the conductive lines may be poly-Si lines or other conductivelines.

Thereafter, in step 130, a grayscale value of the VC difference havingthe blind contact or Quasi-blind issue is compared with a determinedrange of grayscale value to determine whether the VC difference isabnormal. The determined range of grayscale value may be variedaccording to different size of the conductive lines connected to thecontact/via plugs as above conclusion. The size of the conductive linescontains at least one of length, width, area and pitch thereof, forexample. In the embodiment, the determined range of grayscale value isbetween 55 and 130 for finding the so-called Quasi-Blind issue. Bycontrast, the blind grayscale is 0-40 in general.

Furthermore, the first embodiment may be applied to find the contactdefect under the via plugs. For example, in FIG. 4A, it shows that alayout 400 contains metal lines 402 under via plugs 404, and the contactplugs 406 under the metal lines 402. In the layout 400, there are threesites 408 a-c with via plugs and contact plugs.

FIG. 4B shows the VC differences of a chip after forming the via plugs404 of FIG. 4A. Because the via plugs in the site 408 b is located atlong metal line 402, the VC at the site 408 b should be similar to thatat the sites 408 a and 408 c. However, the site 408 b is darker than thesite 408 a or 408 c. After FIB verifies that the via plug 410 at thesite 408 b is normal but the contact plug which connecting with the viaplug 410 is missing, as shown in FIG. 4C.

FIG. 5 is a flowchart of detecting an electrical defect of contact/viaplugs according to the second embodiment of the invention.

In step 500, the contact/via plugs are monitored by using a hot spotinspection, a leap and scan inspection, or a continuous scan inspection,whereby capturing a VC difference in the contact/via plugs. A pixel sizeof the hot spot inspection, the leap and scan inspection, and thecontinuous scan inspection may be less than 0.1 λm for instance. Forexample, the small pixel size may be accomplished by using narroweraperture to converge the electron beam. The hot spot inspection, theleap and scan inspection, and the continuous scan inspection mayrespectively comprise the step of locating same coordinates (x, y) in adesign chip with different dies. In particular, the contact/via plugsmay be both at periphery and array circuits of the different dies, andthe periphery circuit is around the array circuit. Since it will sufferserious misalignment issue by using the continuous or leap and scantraditional E-beam inspection mode with higher resolution and smallinspection field, as shown in FIG. 6A. FIG. 6A shows that leap and scaninspection with positive mode and external electric field hasmisalignment issue in the large inspection field 1536×1536 inspectionfield with pixel 7 nm, and it is hard to achieve better die to dieinspection in the periphery area. However, the hot spot inspection, theleap and scan inspection, and the continuous scan inspection in the step500 can locate the exactly same (x, y) coordinates in the design chipwith different die according the user definition. Therefore, it is noteasy to have image misalignment issue during inspection even using highresolution pixel condition, as shown in FIG. 6B.

FIG. 6B demonstrates the hot spot inspection with small 1536×1536inspection field and with 7 nm pixel resolution, and it shows that theVC differences are identified by comparing the reference die 601 and 602with exactly same location.

In addition, after the step 510, an image extraction is performed on theimage with the VC difference, as described in the first embodiment. Theimage extraction is based on target gray level/back ground gray level.The image extraction may include revising tone to enhance the VCdifference in the step 500, if necessary.

Moreover, one type of VC is found by the hot spot inspection, this typeof VC will become darker than normal one in the first scan, however, itwill back to normal (bright) when do the 2nd inspection, that's named asquasi-blind VC in the embodiment. The quasi-blind VC in these via plugsare induced by the residue on the plug surface, and these residues maybe W and/or O elements, for example. Hence, it is verified that the hotspot inspection can inspect the tiny variation of VC with highsensitivities.

In step 520, the extracted image is contrasted with a layout design baseto obtain a blind contact or Quasi-blind issue of the contact/via plugs.For example, the layout design base comprises a layout containingconductive lines under the contact/via plugs, and the image extractionis utilized to obtain contours of the conductive lines under thecontact/via plugs. As the same with the first embodiment, with aid ofcontact/via layout design base, the blind contact or Quasi-blind issuebecomes easier to distinguish according the correlation of via pluglocations.

Afterwards, in step 530, a grayscale value of the VC difference havingthe blind contact or Quasi-blind issue is compared with a determinedrange of grayscale value to determine whether the VC difference isabnormal. The determined range of grayscale value may be dependent ondifferent size of the conductive lines connected to the contact/viaplugs as above conclusion, wherein the “size” means at least one oflength, width, area and pitch thereof, for example. Furthermore, thetotal grayscale value is 0-255, and the determined range of grayscalevalue is between 55 and 130 to find the Quasi-Blind issue.

Based on the above, in the method of the invention, the layout designbase is used to obtain the blind contact or Quasi-blind issue, and thusit can determine the Quasi-Blind defects by the grayscale valueaccurately. In addition, the Hot Spot inspection, the Leap and Scaninspection, or the Continuous Scan inspection in the invention canresolve the misalignment issue, especially in the irregularly peripheryarea of a chip.

Although the present invention has been described with reference to theabove embodiments, it will be apparent to one of the ordinary skill inthe art that modifications to the described embodiments may be madewithout departing from the spirit of the invention. Accordingly, thescope of the invention is defined by the attached claims not by theabove detailed descriptions.

What is claimed is:
 1. A method for detecting electrical defect ofcontact/via plugs, comprising: monitoring the contact/via plugs by anelectron-beam (E-Beam) inspection tool to capture an image with a VC(voltage contrast) difference; performing an image extraction on theimage with the VC difference, wherein the image extraction is based ontarget gray level/back ground gray level; contrasting the extractedimage with a layout design base to obtain a blind contact or Quasi-blindissue of the contact/via plugs; and comparing a grayscale value of theVC difference having the blind contact or Quasi-blind issue with apredetermined range of grayscale value to determine whether the VCdifference is abnormal.
 2. The method of claim 1, wherein the extractedimage comprises a semi-circular image, a reduced image, or nothing. 3.The method of claim 1, wherein a pixel size of the E-Beam inspectiontool is less than 0.1 μm.
 4. The method of claim 1, wherein thepredetermined range of grayscale value is between 55 and
 130. 5. Themethod of claim 1, wherein the layout design base includes a layoutcontaining conductive lines under the contact/via plugs.
 6. The methodof claim 5, wherein the predetermined range of grayscale value isdependent on different size of the conductive lines connected to thecontact/via plugs.
 7. The method of claim 6, wherein the size of theconductive lines comprises length, width, area or pitch.
 8. The methodof claim 5, wherein the image extraction is utilized to obtain contoursof the conductive lines under the contact/via plugs.
 9. The method ofclaim 1, wherein the image extraction further comprises revising tone ofthe captured image with the VC difference.
 10. A method for detectingelectrical defect of contact/via plug, comprising: using a hot spotinspection, a leap and scan inspection, or a continuous scan inspectionto monitor the contact/via plugs for capturing a VC difference;performing an image extraction on the image with the VC difference;contrasting the extracted image with a layout design base to obtain ablind contact or Quasi-blind issue of the contact/via plugs; andcomparing a grayscale value of the VC difference having the blindcontact or Quasi-blind issue with a predetermined range of grayscalevalue to determine whether the VC difference is abnormal.
 11. The methodof claim 10, wherein the hot spot inspection, the leap and scaninspection, and the continuous scan inspection each comprise locatingsame coordinates in a design chip with different dies.
 12. The method ofclaim 11, wherein the contact/via plugs are both at periphery and arraycircuits of the different dies and the periphery circuit is around thearray circuit.
 13. The method of claim 10, wherein the extracted imagecomprises a semi-circular image, a reduced image, or nothing.
 14. Themethod of claim 10, wherein a pixel size of the hot spot inspection isless than 0.1 μm.
 15. The method of claim 10, wherein a pixel size ofthe leap and scan inspection is less than 0.1 μm.
 16. The method ofclaim 10, wherein a pixel size of the continuous scan inspection is lessthan 0.1 μm.
 17. The method of claim 10, wherein the predetermined rangeof grayscale value is between 55 and
 130. 18. The method of claim 10,wherein the layout design base includes a layout containing conductivelines under the contact/via plugs.
 19. The method of claim 18, whereinthe predetermined range of grayscale value is dependent on differentsize of the conductive lines connected to the contact/via plugs.
 20. Themethod of claim 19, wherein the size of the conductive lines compriseslength, width, area, or pitch.
 21. The method of claim 18, wherein theimage extraction is utilized to obtain contours of the conductive linesunder the contact/via plugs.
 22. The method of claim 10, wherein theimage extraction further comprises revising tone to enhance the VCdifference.